Thin seeded Co/Ni multilayer film with perpendicular anisotropy for read head sensor stabilization

ABSTRACT

A hard bias (HB) structure for producing longitudinal bias to stabilize a free layer in an adjacent spin valve is disclosed and includes a composite seed layer made of at least Ta and a metal layer having a fcc(111) or hcp(001) texture to enhance perpendicular magnetic anisotropy (PMA) in an overlying (Co/Ni) x  laminated layer. The (Co/Ni) x  HB layer deposition involves low power and high Ar pressure to avoid damaging Co/Ni interfaces and thereby preserves PMA. A capping layer is formed on the HB layer to protect against etchants in subsequent process steps. After initialization, magnetization direction in the HB layer is perpendicular to the sidewalls of the spin valve and generates an Mrt value that is greater than from an equivalent thickness of CoPt. A non-magnetic metal separation layer may be formed on the capping layer and spin valve to provide an electrical connection between top and bottom shields.

This is a Divisional application of U.S. patent application Ser. No.12/456,935, filed on Jun. 24, 2009, which is herein incorporated byreference in its entirety, and assigned to a common assignee.

RELATED PATENT APPLICATIONS

This application is related to the following: U.S. Pat. No. 8,064,244,and U.S. Pat. No. 7,804,668; herein incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates to a hard bias structure for stabilizing anadjacent read head sensor and includes a composite seed layer with (111)texture which enhances perpendicular magnetic anisotropy (PMA) in anoverlying laminated Co/Ni hard bias layer.

BACKGROUND OF THE INVENTION

In a magnetic recording device in which a read head is based on a spinvalve magnetoresistance (SVMR) or a giant magnetoresistance (GMR)effect, there is a constant drive to increase recording density. Onemethod of accomplishing this objective is to decrease the size of thesensor element in the read head that is suspended over a magnetic diskon an air bearing surface (ABS). The sensor is a critical component inwhich different magnetic states are detected by passing a sense currentthrough the sensor and monitoring a resistance change. A popular GMRconfiguration includes two ferromagnetic layers which are separated by anon-magnetic conductive layer in the sensor stack. One of theferromagnetic layers is a pinned layer wherein the magnetizationdirection is fixed by exchange coupling with an adjacentanti-ferromagnetic (AFM) pinning layer. The second ferromagnetic layeris a free layer wherein the magnetization vector can rotate in responseto external magnetic fields. In the absence of an external magneticfield, the magnetization direction of the free layer is alignedperpendicular to that of the pinned layer by the influence of hard biaslayers on opposite sides of the sensor stack. When an external magneticfield is applied by passing the sensor over a recording medium on theABS, the free layer magnetic moment may rotate to a direction which isparallel to that of the pinned layer. Alternatively, in a tunnelingmagnetoresistive (TMR) sensor, the two ferromagnetic layers areseparated by a thin non-magnetic dielectric layer.

A sense current is used to detect a resistance value which is lower whenthe magnetic moments of the free layer and pinned layer are in aparallel state. In a CPP configuration, a sense current is passedthrough the sensor in a direction perpendicular to the layers in thesensor stack. Alternatively, there is a current-in-plane (CIP)configuration where the sense current passes through the sensor in adirection parallel to the planes of the layers in the sensor stack.

Ultra-high density (over 100 Gb/in²) recording requires a highlysensitive read head in which the cross-sectional area of the sensor istypically smaller than 0.1×0.1 microns at the ABS plane. Currentrecording head applications are typically based on an abutting junctionconfiguration in which a hard bias layer is formed adjacent to each sideof a free layer in a GMR spin valve structure. As the recording densityfurther increases and track width decreases, the junction edge stabilitybecomes more important so that edge demagnification in the free layerneeds to be reduced. In other words, horizontal (longitudinal) biasingis necessary so that a single domain magnetization state in the freelayer will be stable against all reasonable perturbations while thesensor maintains relatively high signal sensitivity.

In longitudinal biasing read head design, films of high coercivitymaterial are abutted against the edges of the sensor and particularlyagainst the sides of the free layer. In other designs, there is a thinseed layer between the hard bias layer and free layer. By arranging forthe flux flow in the free layer to be equal to the flux flow in theadjoining hard bias layer, the demagnetizing field at the junction edgesof the aforementioned layers vanishes because of the absence of magneticpoles at the junction. As the critical dimensions for sensor elementsbecome smaller with higher recording density requirements but sensorlayer thickness decreases at a slower rate, the minimum longitudinalbias field necessary for free layer domain stabilization increases.

Imperfect alignment with a hard magnetic thin film such as a free layercan give rise to hysteresis or non-linear response of the sensor andthus noise. In general, it is desirable to enhance the coercivity of thehard bias film so that the stray field created by the recording mediumwill not destroy the magnetic alignment of the free layer. A highcoercivity in the in-plane direction is needed in the hard bias layer toprovide a stable longitudinal bias that maintains a single domain statein the free layer and thereby avoids undesirable Barkhausen noise. Thiscondition is realized when there is a sufficient in-plane remnantmagnetization (M_(r)) from the hard bias layer which may also beexpressed as M_(r)t since hard bias field is also dependent on thethickness (t) of the hard bias layer. M_(r)t is the component thatprovides the longitudinal bias flux to the free layer and must be highenough to assure a single magnetic domain in the free layer but not sohigh as to prevent the magnetic field in the free layer from rotatingunder the influence of a reasonably sized external magnetic field.Moreover, a high squareness (S) hard bias material is desired. In otherwords, S=M_(r)/M_(S) should approach 1 where M_(S) represents themagnetic saturation value of the hard bias material.

Longitudinal hard bias structures based on CoPt or CoPtX (X=Cr, B, Ta,etc.) have been commonly used in read head sensor stabilization.However, as the track-width of the sensor becomes smaller and smallertoward higher density recording, the biasing efficiency from thelongitudinal hard bias structure tends to abate. One reason for thedecreased efficiency is because the easy axes of the CoPt magneticgrains tend to distribute randomly in the vicinity of the narrowjunction. In a previous Headway application (U.S. Patent Appl.2008/0117552), we disclosed PMA materials such as CoCrPt or CoCrPtXwhere X may be B, O or other elements that can assist a perpendiculargrowth of the hard bias easy axis to achieve better longitudinal biasingin TMR or CPP-GMR sensors.

Materials exhibiting PMA such as CoPt, CoPt—SiO₂, Tb(Fe)Co, and FePthave been reported multiple times in publications. However, all of theliterature examples suffer from at least one drawback. It is preferredthat establishing a PMA property in a spin valve structure does notrequire strenuous heating. Unfortunately, FePt or Tb(Fe)Co need hightemperature annealing to achieve high enough PMA which is unacceptablefor device integration since certain components are damaged by hightemperatures. CoPt and its alloys such as CoCrPt and CoPt—SiO₂ are notdesirable since a thick seed layer is required to establish a largeenough PMA to stabilize a free layer in an adjacent spin valve element.That leaves the novel magnetic multilayer systems such as Co/X whereX=Pt, Pd, Au, Ni, Ir, and the like for consideration. As stated above,Co/Pt, Co/Pd, and Co/Ir will not be good PMA materials since theyrequire a thick and expensive seed layer made of Pt, Pd, and Ir.Furthermore, Co/Pt, Co/Pd, and Co/Ir configurations typically have smallmagnetic moments due to the inclusion of Pt, Pd, or Ir which arenon-magnetic elements. Au is associated with high cost and easyinterdiffusion to adjacent layers which makes a Co/Au multilayer for PMApurposes less practical. On the other hand, a Co/Ni multilayerconfiguration as a PMA material candidate has several advantagesincluding (a) much higher spin polarization from Co, Ni, and Co/Niinterfaces, (b) better stability from the robustness of Ni layerinsertion, (c) much higher saturation magnetization of 1 Tesla or about2× higher than other Co/M combinations (M=metal), and (d) low cost.

Several attempts disclosed in the literature have been made in order toachieve high PMA from Co/Ni multilayer configurations. However, all ofthe examples typically involve a very thick underlayer to establish PMA.For instance, G. Daalderop et al. in “Prediction and Confirmation ofPerpendicular Magnetic Anisotropy in Co/Ni Multilayers”, Phys. Rev.Lett. 68, 682 (1992) and F. den Broeder et al. in “Co/Ni multilayerswith perpendicular magnetic anisotropy: Kerr effect and thermomagneticwriting”, Appl. Phys. Lett. 61, 1648 (1992), use a 2000 Angstrom thickAu seed layer. In V. Naik et al., “Effect of (111) texture on theperpendicular magnetic anisotropy of Co/Ni multilayers”, J. Appl. Phys.84, 3273 (1998), and in Y. Zhang et al., “Magnetic and magneto-opticproperties of sputtered Co/Ni multilayers”, J. Appl. Phys. 75, 6495(1994), a 500 Angstrom Au/500 Angstrom Ag composite seed layer isemployed. Jaeyong Lee et al. in “Perpendicular magnetic anisotropy ofthe epitaxial fcc Co/60-Angstrom-Ni/Cu(001) system”, Phys. Rev. B 57,R5728 (1997) describe a 1000 Angstrom thick Cu seed layer. A 500Angstrom Ti or 500 Angstrom Cu seed layer with heating to 150° C. isused by P. Bloemen et al. in “Magnetic anisotropies in Co/Ni (111)multilayers”, J. Appl. Phys. 72, 4840 (1992). W. Chen et al. in“Spin-torque driven ferromagnetic resonance of Co/Ni synthetic layers inspin valves”, Appl. Phys. Lett. 92, 012507 (2008) describe a 1000Angstrom Cu/200 Angstrom Pt/100 Angstrom Cu composite seed layer.

The aforementioned thick seed layers are not practical with Co/Nimultilayer PMA configurations in spintronic devices. Typically, there isa space restriction in a direction perpendicular to the planes of thespin valve layers in advanced devices in order to optimize performance.The distance between the substrate and top surface of the spin valvetends to shrink in devices with higher areal density. Likewise, thethickness of the hard bias structure adjacent to the spin valve mustdecrease since it is under similar space restrictions. Seed layersthicker than about 100 Angstroms will require thinning the hard biaslayer to maintain a certain thickness for the hard bias structure whichcan easily lead to lower PMA and less effective biasing because of theMrt relationship. In other words, it is preferable to thin the seedlayer and maintain a maximum thickness in the hard bias layer foroptimum longitudinal biasing efficiency. Therefore, an improved seedlayer is needed that is thin enough to be compatible with high arealdensity devices and yet can induce high PMA in an overlying Co/Nimultilayer in a hard bias structure.

In other prior art references, U.S. Patent Application 2007/0026538describes a hard bias layer made of CoNi but does not include a seedlayer. U.S. Pat. No. 7,134,185 discloses a CoNi hard bias layer which isformed on a Cr or NiAl seed layer. There is no mention in either of theaforementioned references of laminated Co and Ni layers with PMA.

In U.S. Pat. No. 7,433,161, a hard bias structure including a Cr, Ti,Mo, or WMo underlayer, a CoPt or CoCrPt alloy as a hard bias layer, anda Ta interlayer on the hard bias layer is described.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a thin seed layerfor a laminated (R1/R2)_(x) hard bias (HB) layer where x is an integer,R1 is Co or CoFe, and R2 is Ni, NiFe, or NiCo that fully establishes theperpendicular magnetic anisotropy (PMA) in the overlying (R1/R2)_(x)stack without requiring a heat treatment that could degrade othercomponents in an adjacent spin valve element.

A second objective of the present invention is to provide a hard biasstructure comprised of a thin seed layer and overlying (R1/R2)_(x) hardbias layer that achieves high Hk of over 15000 Oe, a squareness ofnearly 1, and an Mrt value higher than that of a CoPt layer with thesame thickness.

A third objective of the present invention is to provide a method offorming a laminated (R1/R2)_(x) stack in a hard bias structure so theface centered cubic (fcc) (111) super lattice in the R1 and R2 layersand the interface between adjacent R1 and R2 layers is preserved.

According to one embodiment, these objectives are realized by firstproviding a spin valve element (TMR or CPP-GMR sensor) on a substratesuch as a bottom shield in a read head. The spin, valve element has atop surface and sidewalls that connect the top surface to the substrate.In one aspect there is an isolation layer made of metal oxide, metalnitride, or metal oxynitride formed on the substrate and along thesidewalls of the spin valve element. Above the isolation layer is a hardbias structure comprised of a composite seed layer and a[R1(t1)/R2(t2)]_(x) (laminated HB layer formed on the seed layer where xis from about 10 to 70 depending on the Mst requirement, and t1 and t2are the thicknesses of the R1 and R2 layers, respectively. Thus, thereare horizontal sections of the seed layer formed on portions of theisolation layer which lie in a plane parallel to the substrate. Further,there are sloped sections of the seed layer formed along a plane that isparallel to the sloped sidewalls of the sensor. In the laminated HBlayer, each of the R1 layers has a thickness (t1) from 0.5 to 5Angstroms and each of the R2 layers has a thickness (t2) of 2 to 10Angstroms where t2 is preferably greater than t1. The seed layerpreferably has a Ta/M1/M2 or Ta/M1 configuration where M1 is a metalsuch as Ru having a fcc(111) or (hcp) hexagonal closed packed (001)crystal orientation, and M2 is Cu, Ti, Pd, W, Rh, Au, or Ag. In the caseof Pd, Au, and Ag, the M2 layer thickness is kept to a minimum in orderto reduce cost. Ta and M1 layers in the composite seed layer arecritical for enhancing the (111) texture in overlying HB layers.

A key feature is growth of the laminated HB layer on the seed layer suchthat the easy axis of the laminated HB layer is oriented perpendicularto the seed layer. Following HB initialization, HB magnetization nearthe sensor will be along the easy axis and perpendicular to the nearbysidewall of the sensor, resulting in surface charges as close aspossible to the free layer. Body charges in regions of the HB layeralong horizontal sections of seed layer are not significant and onlycharges from grains formed on sloped seed layer sections along thesloped sensor sidewalls are major contributors to the hard bias field.

Above the hard bias layer is a capping layer that is preferably made ofTa. The capping layer serves to protect the hard bias structure fromsubsequent process steps that may involve a chemical mechanical polish(CMP) process, an ion beam etch, or other etches. A non-magneticseparation layer made of a metal such as Ru is formed on the cappinglayer and contacts the top surface of the sensor element. A top shieldis disposed on the non-magnetic separation layer and serves as a toplead that is electrically connected to the bottom shield (bottom lead)through the non-magnetic separation layer and sensor element.

An important feature of all embodiments is that each of the R1 and R2layers in the (R1/R2)_(x) laminate is deposited with a very low RF powerand a high inert gas pressure to minimize the impinging ion energy sothat deposition of a layer does not damage the R1 or R2 layer on whichit is formed. Thus, in an example where R1 is Co and R2 is Ni, theinterfaces between the Co and Ni layers are preserved to maximize thePMA property. Furthermore, this method enables the PMA of (Co/Ni)_(x) or(R1/R2)_(x) laminates to be preserved with a substantially thinner seedlayer. The isolation layer and all layers in the hard bias structure maybe formed in a magnetron sputtering system containing depositionchambers and at least one oxidation chamber. After the capping layer isdeposited, the top surface of the hard bias structure may be planarizedsuch that a portion of the capping layer and hard bias layer proximateto the sensor sidewalls is essentially coplanar with the top surface ofthe sensor element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a spin valve structure formedon a substrate according to one embodiment of the present invention.

FIG. 2 is cross-sectional view of a hard bias structure formed adjacentto a sidewall in the spin valve shown in FIG. 1 wherein the arrows inthe hard bias layer indicate the easy axes orientation according to afirst embodiment of the present invention.

FIG. 3 is cross-sectional view of the hard bias structure in FIG. 2 inwhich the arrows indicate the longitudinal biasing direction of the hardbias layer after the hard bias layer is initialized according to anembodiment of the present invention.

FIGS. 4 a-4 d are MH curves showing the effect of Cu seed layerthickness on the PMA in an overlying (Co/Ni)₂₀ multilayer structure.

FIGS. 5 a-5 d are MH curves showing how the Cu thickness in a Ta/Ru/Cucomposite seed layer affects the PMA in an overlying (Co/Ni)₂₀multilayer structure.

FIGS. 6 a-6 c are plots with MH curves showing how the Cu layer in aTa/Ru/Cu composite seed layer can be thinned or removed while stillpreserving the PMA in an overlying (Co/Ni)_(x) laminated structureaccording to one embodiment of the present invention.

FIG. 7 is a plot with MH curves illustrating how the Ta and Ru layers inthe Ta/Ru composite seed layer in FIG. 6 c can be thinned while stillmaintaining PMA in an overlying Co/Ni laminated structure according toan embodiment of the present invention.

FIG. 8 is a plot with MH curves showing the effect of annealing on thePMA in a Ta30/Ru50/Cu100/[Co(2)/Ni(5)]₂₀ multilayer hard bias structurewith a Ru10/Ta40/Ru30 capping layer formed according to an embodiment ofthe present invention.

FIG. 9 is a plot with MH curves for a Ta10/Ru²⁰/Cu10/[Co2/Ni4]×30 hardbias structure with a Ta capping layer according to one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a hard bias structure for providinglongitudinal bias to a free layer in an adjacent CPP-GMR or TMR spinvalve structure and includes a thin composite seed layer formed on asubstrate and a (R1/R2)_(x) laminated hard bias layer with perpendicularmagnetic anisotropy. PMA is fully established with a thin composite seedlayer comprised of a lower Ta layer and an upper metal layer withfcc(111) or hcp(001) crystal orientation for enhanced performance. Thepresent invention also includes a method of depositing the (R1/R2)_(x)laminated hard bias layer such that the R1/R2 interfaces are wellpreserved and only a thin seed layer is required for establishing thedesired fcc(111) orientation. Drawings are provided by way of exampleand are not intended to limit the scope of the invention.

In principle, the magnetic anisotropy of a hard bias layer such as a(Co/Ni)_(x) laminated structure arises from the spin-orbit interactionsof the 3d and 4s electrons of Co and Ni atoms. Such interaction causesthe existence of an orbital moment which is anisotropic with respect tothe crystal axes which are in (111) alignment, and also leads to analignment of the spin moment with the orbital moment. In (Co/Ni)_(x)laminated structures, it is essential to have a fcc (111) super-latticein order to establish PMA. As mentioned previously, prior art structuresrely on assistance from a thick seed layer having a perfect fccstructure such as Au, Au/Ag, Ti, Cu, and Au/Cu to establish PMA in a(Co/Ni)_(x) multilayer configuration. In the G. Daalderop and F. denBroeder references mentioned previously, it is believed that the PMAeffect is established by the presence of an interface between ultra-thinlayers of closed packed Co and Ni atoms. Since Co and Ni differ only byone valence electron, the existence of Co and Ni interfaces will giverise to a large magnetic anisotropy.

In the present invention, we have discovered a method for depositing R1and R2 layers that preserves the interfaces of the laminated R1 and R2layers thereby requiring a substantially thinner seed layer for hardbias structures. Moreover, once the number of laminations (x) in a(Co/Ni)_(x) layer, for example, disclosed herein reaches a large enoughnumber between about 10 and 70, there is a sufficient quantity of Co andNi valence electrons to generate a high PMA from the spin-orbitinteractions and thereby stabilize a free layer in an adjacent spinvalve structure. In one aspect, a composite seed layer represented byTa/M1 where M1 is an upper metal layer having a fcc(111) or hcp(001)crystal orientation such as Ru, Cu, or Au provides an additionaladvantage of enhancing the (111) texture in an overlying hard biasstructure thereby optimizing the PMA in the laminated hard bias layer.

First, various embodiments of a (R1/R2)_(x) hard bias structure havinghigh PMA according to the present invention will be described and then amethod for forming a (Co/Ni)_(x) laminated structure which preserves theCo/Ni interfaces will be provided.

Referring to FIG. 1, a portion of a sensor stack in a read headstructure 30 is shown as viewed from an air bearing surface (ABS) plane.A bottom shield 1 made of permalloy, for example, is formed on asubstrate (not shown) that is typically ceramic and a patterned spinvalve element (sensor) is formed on the bottom shield by a well knownmethod. According to the exemplary embodiment of the present invention,the sensor is a bottom spin valve having a bottom layer 6 comprised of acomposite such as a seed layer contacting the bottom shield 1 and an AFMlayer formed on the seed layer. Seed and AFM layers are not shown tosimplify the drawing. Above the bottom layer 6 is sequentially formed areference layer 7, a non-magnetic spacer or tunnel barrier 8, a freelayer 9, and a capping layer 10. Capping layer 10 may be a compositemade of two or more layers and may include an upper layer that serves asa hard mask during patterning of the sensor stack of layers to form aspin valve element. The compositions of the layers within the sensor arenot described because the present invention encompasses all materialsused to fabricate layers therein and which are well known to thoseskilled in the art. The sensor has a top surface 10 a, a sidewall 20along a first side, and a second sidewall 21 along a side opposite tothe first side. From a top-down view (not shown), the top surface 10 aof the sensor may appear as a circle, ellipse, or a polygonal shape.

In another embodiment (not shown), the spin valve element may be a topspin valve or a dual spin valve as appreciated by those skilled in theart. At least one free layer in the top spin valve or dual spin valvewill require stabilization by a hard bias structure of the presentinvention.

Referring to FIG. 2, an isolation layer 3 made of AlOx or anotherdielectric material has sections 3 a and 3 b formed on the bottom shield1 and along sidewall 20 (and 21), respectively. There is a thincomposite seed layer 22 (individual layers not shown) disposed on theisolation layer 3. A key feature is the composite seed layer 22 has afcc(111) lattice and may be comprised of a Ta/Ru/Cu configuration wherea lower Ta layer having a thickness of 5 to 100 Angstroms contactsisolation layer 3, a middle Ru layer about 10 to 100 Angstroms thick isformed on the Ta layer, and an upper Cu layer 1 to 100 Angstroms thickis formed on the Ru layer. In another aspect, the upper Cu layer may beremoved and a Ta/Ru composite seed layer 22 is employed wherein the Taand Ru layers have thicknesses of 5 to 100 Angstroms, and 10 to 100Angstroms, respectively. Optionally, Ru may be replaced by a metal M1layer having a fcc(111) or hcp(001) lattice structure.

In another embodiment, the upper Cu layer in the composite seed layer 22may be replaced by a metal M2 such as Ti, Pd, W, Rh, Au, Ag, or the likewith a thickness for M2 of from 1 to 100 Angstroms to give a Ta/M1/M2configuration where M1 is unequal to M2. However, it is critical thatthe composite seed layer 22 be comprised of a lower Ta layer and atleast one metal layer having fcc(111) or hcp(001) crystal orientation onthe Ta layer to enhance the (111) crystal structure in an overlying(R1/R2)_(x) laminated layer and enhance the PMA therein. In anotherembodiment, the composite seed layer may comprise NiCr and at least oneof Ta and Ru.

Above the composite seed layer 22 is a hard bias layer 25 thatpreferably has a (R1/R2)d_(x) laminated structure where R1 is Co orCoFe, R2 is Ni, NiFe, or NiCo, and x is between about 10 and 70depending on the Mst requirement. Preferably, CoFe has a compositionrepresented by Co_((100-w))Fe_(w) where w is from 0 to 90 atomic %, NiFehas a composition represented by Ni_((100-y))Fe_(y) where y is from 0 to50 atomic %, and NiCo has a composition represented byNi_((100-z))Fe_(z) where z is from 0 to 50 atomic %. Each of theplurality of R1 layers in the laminated hard bias layer 25 has athickness from 0.5 to 5 Angstroms, and preferably between 1.5 to 3Angstroms. Each of the plurality of R2 layers in the laminated hard biaslayer has a thickness from 2 to 10 Angstroms, and preferably between 3.5and 8 Angstroms. Preferably, the thickness t2 of a R2 layer is greaterthan a R1 layer thickness t1, and more preferably, t2˜2X t1 in order tooptimize the spin orbit interactions between adjacent R1 and R2 layers.In addition, R1 and R2 layers are preferably deposited by a method thatpreserves the R1/R2 interfaces as described in a later section. In oneaspect, when t1 is less than or equal to about 2 Angstroms, the R1 layermay be considered as a “close-packed” layer and not necessarily having a(111) crystal orientation.

FIG. 2 also depicts arrows 40 a representing the easy axis of HB grainsformed on the seed layer 22 above isolation layer 3 a and arrows 40 brepresenting the easy axis of HB grains formed on the seed layer aboveisolation layer 3 b. With the easy axes 40 a, 40 b orientedperpendicular to the underlying seed layer 22, initialization of the HBlayer 25 can be achieved by applying a strong in-plane longitudinalfield along the x-axis direction (left to right) that overcomes theanisotropy field of the HB material and aligns the HB magnetization inthe same direction as the applied field. Once the field is withdrawn,the magnetizations of the HB grains relax to the uniaxial easy axisdirection that has a smaller angle to the longitudinal direction. HBinitialization preferably occurs after atop shield 2 has been formed.For HB grains grown along the sidewall 20, the magnetization will be inthe direction along the easy axis direction but pointing toward thesidewall 20. Therefore, the charges (not shown) from the HB layer 25 aremainly surface charges from these edge grains inside region 23. Thischarge placement is actually the best situation for generating a strongHB field in the sensor stack and free layer 9 because the charges are atthe closest position to the sensor stack (sidewall 20) and the solidangle (not shown) from the charges is maximized.

For HB grains grown above isolation layer 3 a, their easy axis isperpendicular to the top surface 1 a of the bottom shield 1 as indicatedby arrows 40 a and the orientation of the magnetization is theoreticallyrandom after HB initialization. Charges will be formed near theinterface of HB layer 25 with seed layer 22 and capping layer 11 inregions above isolation layer 3 a. Random magnetization is not a concernin these regions, however, since the solid angles formed by grainstherein relative to the free layer 9 are much smaller than those grownabove isolation layer 3 b near sidewall 20. Therefore, the charges inthe HB layer 25 above isolation layer 3 a will be much smaller than thesurface charges in region 23. A second consideration regarding randommagnetization is that if the sensor stack and particularly the freelayer 9 is positioned near the center plane (not shown) of the HB layer25, the field from the net charge, if any, on the top and bottomsurfaces of the HB layer above insulating layer 3 a will cancel eachother as they are exactly the opposite sign and of the same magnitude.It should be understood that the HB layer 25 on the opposite side of thesensor stack has a magnetization along sidewall 21 (FIG. 3) that isequal to the magnetization at sidewall 20 but pointing in a directionaway from sidewall 21.

It is reasonable to think that the HB regions where the two differenteasy axis growth patterns meet will be an area where an amorphous phasemay arise and cause variations in the HB field. However, this hard biasscheme does not depend on body charges to generate an HB field in thefree layer 9. Moreover, the HB layer 25 thickness can be greatly reducedto minimize the effect of the amorphous phase in a region where arrows40 a and 40 b intersect.

The uppermost layer in the hard bias structure is a capping layer 26. Inone aspect, the capping layer 11 is comprised of Ta with a thickness inthe range of 40 to 80 Angstroms. Alternatively, the capping layer mayinclude Ta and at least one layer of Ru as in a Ru/Ta/Ru configuration.Ru may be employed because of its oxidation resistance. Ta is preferredbecause it offers good protection against wet etchants and dry etchantsin subsequent processing steps such as a CMP process or an ion beametching (IBE) step. Optionally, other capping layer materials used inthe art may be used as capping layer 26. Note that a top portion ofcomposite seed layer 22, a top surface 25 s of hard bias layer 25 formedalong sidewall 20, and a portion of capping layer 26 are essentiallycoplanar with top surface 10 a of the spin valve element.

There is a non-magnetic separation layer 11 made of Ru or the likeformed on top surface 10 a, top surface 25 s, and on the capping layer26 to prevent a magnetic interaction between top shield 2 and hard biaslayer 25. Non-magnetic separation layer 11 forms an excellent electricalconnection between top shield 2 and capping layer 10 in the sensorelement. In one embodiment, non-magnetic separation layer 11 is notplanar and instead conforms to the shape of underlying layers. Forexample, a portion of non-magnetic separation layer 11 above top surface10 a and top surface 25 a is a greater distance from bottom shield 1than portions formed above sections of hard bias layer 25 having easyaxes 40 a.

Next, a top shield 2 may be formed on the non-magnetic separation layer11 by a conventional method. Top shield 2 may be made of the samepermalloy as in bottom shield 1.

Referring to FIG. 3, the magnetization in hard bias layer 25 proximateto sidewall 20 is depicted by arrows 24 b and proximate to sidewall 21by arrows 24 c following hard bias initialization along the (+)x axisdirection. Magnetization 24 c is perpendicular to sidewall 21 but pointsaway from the sidewall. The magnetization 24 b, 24 c in hard bias layer25 provides essentially all of the longitudinal biasing to free layer 9.Note that magnetization 24 a in hard bias layer 25 above horizontalsections of isolation layer 3 a is random and does not contribute tofree layer stabilization.

With regard to a process of forming the hard bias structures in theaforementioned embodiments, the isolation layer 3 and all of the layersin the hard bias structure 50 may be laid down in a sputter depositionsystem after a single pump down step. For instance, isolation layer 3,seed layer 22, hard bias layer 25, and capping layer 26 may be formed inan Anelva C-7100 thin film sputtering system or the like which typicallyincludes physical vapor deposition (PVD) chambers, an oxidation chamber,and a sputter etching chamber. Typically, the sputter deposition processinvolves an argon sputter gas with ultra-high vacuum and the targets aremade of metal or alloys to be deposited on a substrate. In analternative embodiment, isolation layer 3 may be formed by a PVD orchemical vapor deposition method in a separate deposition tool.

The present invention also encompasses an annealing step after alllayers in the hard bias structure have been deposited. The hard biasstructure 50 may be annealed by applying a temperature between 200° C.and 280° C. for a period of 0.5 to 10 hours. No applied magnetic fieldis necessary during the annealing step because PMA is established due tothe (111) texture in the composite seed layer 22 and due to the spinorbital interactions between R1 and R2 layers in the laminated hard biaslayer 25.

An important feature of the present invention is the method fordepositing the (R1/R2)_(x) laminated hard bias layer 25. Although thefollowing description relates to R1=Co, and R2=Ni, those skilled in theart will appreciate that the same process may be applied where R1 isCoFe and R2 is NiFe or NiCo. In particular, a lower RF power and high Arpressure are utilized to avoid damaging the substrate on which each Coor Ni layer is deposited in order to preserve the resulting Co/Ni(R1/R2) interfaces and enhance the PMA property therein. In other words,the ion energy impinging on recently deposited Co and Ni surfaces isminimized during sputter deposition of subsequent Co and Ni layers toreduce damage from ion bombardment during the sputtering process. In oneembodiment, each of the Co and Ni layers in the laminated hard biaslayer 25 is laid down in a DC magnetron sputter deposition chamber by aprocess comprising a RF power of less than 200 Watts, and an Ar flowrate of >15 standard cubic centimeters per minute (sccm). Deposition ofeach Co and Ni layer requires less than a minute and total timenecessary to form a (Co/Ni)₂₀ structure is less than about an hour.

It should be understood that a photoresist layer is initially formed onthe sensor stack of layers and is patterned before serving as an etchmask while the spin valve is patterned and sidewalls defined by one ormore etching steps. The photoresist mask typically remains on thepatterned sensor during deposition of the isolation layer and hard biasstructure 50. Furthermore, in order to achieve a uniformly thick HBlayer 25 on a seed layer 22 with topography as depicted in the preferredembodiments (FIGS. 2-3), it may be necessary to perform the seed layerdeposition and HB deposition in more than one step. For example, a firststep may involve a high deposition angle while a second step employs alow deposition angle. To minimize the overspray, a shaper may be used inIBD systems. The present invention also anticipates that a portion ofthe hard bias layer or capping layer may be removed by an ion beam etch.As a result of the hard bias structure 50 deposition sequence andoptional ion beam etch thereafter, top shield 2 is generally thicker inregions above HB layer 25 having easy axes 40 a than above the topsurface 10 a and top surface 25 s. Typically, the photoresist mask isremoved after the HB layer 25 and capping layer 26 are formed.

Once all the layers in the hard bias structure 50 are formed, a mild CMPprocess may be employed to planarize the top surface 25 s so that hardbias layer 25 in regions having easy axes 40 b and capping layer 26 areessentially coplanar with the top surface 10 a. Thereafter, anon-magnetic separation layer 11 may be deposited on the hard bias layer25 and top surface 10 a. Top shield 2 is formed on the non-magneticseparation layer by a conventional method such as a plating operation.

Example 1

An experiment was conducted to demonstrate the effectiveness of forminga (Co/Ni)_(x) laminated hard bias layer with regard to minimizing therequired thickness of the seed layer in a hard bias structure. A stackcomprised of a Cu seed layer, (Co/Ni)₂₀ laminated layer where each Colayer is 2 Angstroms thick and each Ni layer is 4 Angstroms thick, and aRu10/Ta40/Ru30 cap layer was fabricated in order to obtain PMA valuesfrom MH curves using a vibrating sample magnometer (VSM). The thicknessof each layer in the composite cap layer is shown by the numberfollowing each of the elements. Copper seed layer thickness was reducedfrom 1000 Angstroms in FIG. 4 a to 500 Angstroms in FIG. 4 b, 200Angstroms in FIG. 4 c, and to 100 Angstroms in FIG. 4 d. The upper plotin each figure shows the horizontal to plane component of each magneticfield and the lower plot in each figure illustrates the perpendicularmagnetic anisotropy (PMA) component. It should be understood that thedistances s₁-s₄ between the mostly vertical sections in the lower plotsare proportional to the PMA magnitude. Clearly, PMA can be maintainedeven with a Cu seed layer as thin as 100 Angstroms although PMAdecreases somewhat as the Cu seed layer is thinned. Furthermore, fromtorque measurements, we deduced that Hk for each (Co/Ni)₂₀ stack havinga 100 Angstrom thick Cu seed layer is >15000 Oersted (Oe).

Example 2

In a second experiment, a Ta/Ru underlayer was inserted to form aTa/Ru/Cu seed layer and further enhance the (111) texture of the upperCu layer according to an embodiment of the present invention where theseed layer is represented by Ta/M1/M2 and M1 is unequal to M2. The lowerTa layer thickness is 30 Angstroms and the middle Ru layer thickness is20 Angstroms. The other layers in the hard bias stack have the samecomposition and thickness as indicated in the previous example. As aresult, PMA is further improved with respect to FIGS. 4 a-4 d asindicated by the MH curves in FIGS. 5 a-5 d. Note that the distance s₅in FIG. 5 c is greater than s₄ where the Cu layer in both cases is 100Angstroms thick and indicates larger PMA in an overlying (Co/Ni)_(x)hard bias layer when a Ta/Ru/Cu seed layer is employed. Those skilled inthe art will also recognize that the sloped portions of the curves inFIGS. 5 a-5 d are more vertical than the sloped portions in FIGS. 4 a-4d which represents improved perpendicular magnetic properties. Thethickness of the upper Cu layer in the composite seed layer is reducedfrom 2000 Angstroms in FIG. 5 a, to 200 Angstroms in FIG. 5 b, 100Angstroms in FIG. 5 c, and to 50 Angstroms in FIG. 5 d. Even with a thin50 Angstrom Cu layer (FIG. 5 d), there is a PMA improvement over FIG. 4a representing the thick (1000 Angstrom) Cu seed layer. Hk is confirmedby torque measurements to be larger than 15000 Oe even with a very thinTa30/Ru20/Cu50 seed layer.

Example 3

To further explore the effect of thinning the upper Cu layer in thecomposite seed layer described in Example 2, the upper Cu layer wasthinned from 50 Angstroms in FIG. 6 a to 30 Angstroms in FIG. 6 b, andcompletely removed in FIG. 6 c. Note that the resulting seed layer has a30 Angstrom thick Ta layer and a 50 Angstrom thick Ru layer in the Ta/Ruconfiguration and represents a Ta/M1 seed layer according to anotherembodiment of the present invention. In addition, the thickness of eachNi layer in the (Co/Ni)₂₀ hard bias stack was increased slightly to 5Angstroms. We have found that excellent PMA properties are retained inthe (Co/Ni)₂₀ multilayer even when the Cu layer in the composite seedlayer is removed as illustrated in FIG. 6 c.

Example 4

A stack comprised of a Ta30/Ru50/Cu100 composite seed layer, a middle(Co/Ni)₂₀ laminated layer, and an upper composite Ru10/Ta40/Ru30 caplayer was annealed at 220° C. for 2 hours. No applied magnetic fieldduring annealing is necessary to establish PMA. However, PMA doesincrease substantially during the annealing step as indicated in FIG. 7where the left side of the figure depicts MH curves for parallel (upper)and perpendicular (lower) magnetic components prior to annealing and theright side of the figure shows the MH curves after the annealingprocess. Each of the Co layers has a 2 Angstrom thickness and each ofthe Ni layers has a 5 Angstrom thickness in FIG. 7. Typical Ku and Hkresults from an annealed structure such as the one described above areabout 5.64E+06 erg/cc and 17161 Oe, respectively.

Example 5

According to a preferred embodiment of the present invention, a hardbias structure was fabricated on an AlOx substrate to characterize theperformance. The HB structure was made with the following configurationin which the value following each individual layer represents the filmthickness in Angstroms: Ta10/Ru20/Cu10/[(Co2/Ni4)₃₀]/Ta60. In theaforementioned structure, Ta/Ru/Cu is the composite seed layer, theCo/Ni laminate is the hard bias layer, and a 60 Angstrom thick Ta layeris the capping layer. FIG. 8 illustrates a MH curve for the parallel toplane magnetic anisotropy component (upper plot) and a MH curve for thePMA component (lower plot). It is clearly shown that the PMA of the(Co/Ni)₃₀ laminated hard bias layer is well preserved. With Hk>15000 Oe,Mrt>2 memu/cm², and a squareness S of about 1, a good biasing effect isexpected when this hard bias structure is employed for free layerstabilization in a GMR-CPP or TMR sensor. Note that the laminationnumber (x=30 in this example) may be increased or decreased depending onthe actual free layer moment so that the optimum biasing effect can beachieved.

Example 6

According to another embodiment of the present invention, a hard biasstructure including a Ta/Ru seed layer was fabricated on an aluminumoxide substrate to characterize the performance in which the valuefollowing each individual layer represents the film thickness inAngstroms: Ta10/Ru20/[(Co2/Ni4)₃₀]Ta60. In this configuration, a thinnerseed layer is used to further improve the biasing field by enabling thehard bias layer to comprise a greater proportion of the overall hardbias structure. The (Co/Ni)₃₀ laminated hard bias layer grows on theTa/Ru seed layer such that its easy axes are aligned perpendicular tothe seed layer as indicated in FIG. 2. FIG. 9 clearly shows the PMA ofthe (Co/Ni)₃₀ hard bias layer is well preserved. Again, the Hk>15000,Mrt>2 memu/cm², and squareness is about 1 for an excellent biasingeffect. In comparison, a CoPt layer would require a thickness of 200Angstroms to have an equivalent Mrt value to the 180 Angstrom thick(Co/Ni)₃₀ laminated layer. Actual magnitude of the biasing field mayvary depending on the lamination number selected. For example, greaterbiasing power can be achieved by increasing the value of x or increasingthe thicknesses t1, t2 of the Co and Ni layers, respectively.

We have described various embodiments of hard bias structures having athin seed layer such as Ta/Ru or Ta/Ru/Cu with a fcc(111) latticeconfiguration that produces outstanding perpendicular magneticanisotropy and longitudinal biasing strength in an overlying (Co/Ni)_(x)laminated hard bias layer. The resulting biasing field is greater thanthat afforded by an equivalent thickness of CoPt or alloys thereof.Biasing strength is easily adjusted by varying the lamination number“x”. A deposition method for Co and Ni films is described that preservesthe Co/Ni interfaces in the hard bias laminate and thereby maintains PMAto provide optimum performance.

While this invention has been particularly shown and described withreference to, the preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of this invention.

We claim:
 1. A magnetic read head, comprising: (a) a bottom shieldhaving a top surface; (b) a sensor element having a plurality of layersincluding a free layer formed therein, said sensor element has a topsurface, sidewalls, and contacts the top surface of the bottom shield;(c) a metal oxide, metal nitride, or metal oxinitride isolation layerformed on the top surface of the bottom shield in regions adjacent tothe sensor element and along the sidewalls of the sensor element; (d) acomposite seed layer including at least a lower Ta layer formed on theisolation layer, and a metal (M1) layer having a fcc(111) or hcp(001)crystal structure disposed on the lower Ta layer; said composite seedlayer has a horizontal section formed in a plane parallel to the topsurface of the bottom shield, and a second section formed proximate tosaid sidewalls and connected to the horizontal section; (e) a(R1/R2)_(x) laminated hard bias layer having inherent PMA and formed onthe composite seed layer where R1 is Co or CoFe, R2 is NiFe or NiCo, xis an integer, and wherein a thickness (t2) of each R2 layer is greaterthan a thickness (t1) of each R1 layer; (f) a capping layer formed onthe (R1/R2)_(x) laminated hard bias layer; (g) a non-magnetic separationlayer formed on the capping layer and contacting the top surface of thesensor element; and (h) a top shield on the non-magnetic separationlayer that is electrically connected to the bottom shield through thenon-magnetic separation layer and sensor element.
 2. The magnetic readhead of claim 1 wherein x is from about 10 to 70, the thickness t1 isfrom about 0.5 to 5 Angstroms, and the thickness t2 is between about 2and 10 Angstroms.
 3. The magnetic read head of claim 1 wherein the lowerTa layer has a thickness from about 5 to 100 Angstroms and the metal(M1) layer with fcc(111) or hcp(001) crystal orientation has a thicknessbetween about 10 to 100 Angstroms and is comprised of Ru, Cu, or Au. 4.The magnetic read head of claim 1 wherein the composite seed layer isfurther comprised of a metal layer M2 that is one of Cu, Ti, Pd, W. Rh,Au, or Ag and formed on the M1 layer to give a Ta/M1/M2 configuration inwhich the lower Ta layer thickness is from about 5 to 100 Angstroms, theM1 layer thickness is between about 10 and 100 Angstroms, the metal M2layer thickness is from about 1 to 100 Angstroms, and M1 is unequal toM2.
 5. The magnetic read head of claim 1 wherein the non-magneticseparation layer is comprised of Ru and has a thickness between about 15and 100 Angstroms.
 6. The magnetic read head of claim 1 wherein thecapping layer is comprised of Ta and has a thickness from about 40 to 80Angstroms.
 7. The magnetic read head of claim 1 wherein CoFe has acomposition by Co_((100-w))Fe_(w) where w is from 0 to about 90 atomic%, NiFe has a composition represented by Ni_((100-y))Fe_(y) where y isfrom 0 to about 50 atomic %, and NiCo has a composition represented byNi_((100-z))Fe_(z) where z is from 0 to about 50 atomic %.